SECTION III 





THE BLOOD PLATELETS 



THE very existence of these, the third class of formed elements of the 



blood, is still a matter of dispute. If a drop of osmic acid be placed on the 



finger, which is then pricked through 



the drop so that the shed blood may 



mix with the fixing fluid directly it 



leaves the vessels, a drop of the mixture 



when examined under high powers is 



seen to present a number of granular 



bodies from one-third to one-half the 



diameter of a red blood corpuscle. Their 



number has been variously stated from 



180,000 to 800,000 per cubic millimetre, 



so that they rank second in point of 



i r i i FIG. 378. Blood platelets, highly mag- 



number among the morphological con- nified, showing the amoeboid for^s 



stituents of the blood. Their shape 



varies considerably. Some are bi-convex 



structures ; others are flatter with numerous 



processes. They may be isolated or 



agglutinated into clumps. Their shape, 



size, and number vary according to the fluid with which the blood is 



mixed or the method adopted for their demonstration. 



When blood is examined in Hayem's fluid * nearly all the blood platelets appear 

 as bi-convex discs. The best method for the display of platelets is apparently that 

 given by Deetjen. The drop of blood is received directly from the vessels on to a sheet 

 of solid agar jelly which is made with 0-6 per cent, sodium chloride solution with the 

 addition of sodium metaphosphate and bipotassium phosphate. When examined on 

 this medium large numbers of platelets are seen, each of them provided with numerous 

 processes (Fig. 378). Their central part is more strongly refracting than the periphery 

 and stains with basic dyes, so that it has been regarded as a nucleus. 



Similar platelets are observed when the blood is received into normal 

 salt solution; as the mixture clots, the filaments of fibrin can be seen 



which they assume when examined 

 under suitable conditions, and also 

 exhibiting the chromatic particle 

 which each platelet contains, and 

 which has been regarded as a 

 nucleus. (After KOPSCH.) 



1 Hayem's fluid is made up as follows : 

 Distilled water . 

 Sodium chloride 

 Sodium sulphate 

 Iodine in iodide of potassium 

 879 



200 c.c. 

 1 grm. 

 5 grm. 

 3-5 c.c. 



